Changes in sleep-waking rhythms of rats following a single injection of toluene.

Abstract

The acute effects of toluene on sleep-waking rhythms were investigated in rats. In order to determine the characteristics of sleep-waking rhythms in rats quantitatively, polygraphic recordings of cortical EEG activity and neck EMG were made under a 12 : 12 light-dark schedule. Toluene was injected intraperitoneally at three dosages, i.e., 200, 400 and 600 mg/kg of body weight. The toluene con-centration in the blood was determined in rats implanted with a jugular catheter to collect the blood. The circadian sleep-waking rhythms were still entrained to the environmental light-dark cycle following the administration of toluene. On the day of administration, wakefulness (W) increased immediately after toluene administration at the lower two doses, and an abnormal EEG pattern was observed transiently at the highest dose. The initial increase in W at 200 and 400 mg/kg and the appearance of the abnormal EEG pattern at 600 mg/kg were observed for 32, 79 and 83 min. after the administration of toluene, respectively. The toluene concentration in the blood of rats given 600 mg/kg was about 70 μg/ml when the abnormal EEG disappeared. Slow wave sleep (SWS) and paradoxical sleep (PS) increased during the period when blood toluene levels decreased. On the second day, when almost all of the toluene was eliminated from the blood, the lowest dose produced an increase in PS during the dark period, and the higher two doses produced a decrease in PS during the light period. At the highest dose, the amount of SWS during the light period was still higher than control. Toluene-induced changes in the sleep-waking rhythms returned to the control by the third day.